FIGS. 1 and 2 are schematic views showing a whole and particulars of a conventional valve guide structure, respectively.
Generally, a valve 1 of an engine has a vertically extending stem 2 pinched and supported by an inner peripheral surface 4 of a sleeve-like valve guide 3. Arranged on an upper end of the stem 2 via a cross head 5 is a rocker arm 6 so as to transmit vertical motions to the valve 1.
The cross head 5 has a guide pin 7 arranged substantially centrally on the head 5 to restrict movements of the rocker arm 6 to the valve 1 to vertical directions. The valve guide 3 in support of the valve 1 is fixed to a cylinder head 8 to further restrict the moving directions of the valve 1 to the vertical directions.
An outer peripheral surface of the valve guide 3 is formed, at its upper portion, with a smaller-diameter outer peripheral surface 9 for arrangement having an annular engagement groove 10 on the surface 9. The peripheral surface 9 and the engagement groove 10 are engaged with a cylindrical stem seal 11 which in turn has at its top a closed portion 12 in abutment with the stem 2 of the valve 1 and a spring 13 for tightening the closed portion 12 to prevent intrusion of oil. In the figures, reference numeral 14 denotes valve springs urging the valve 1 into a closed direction; and 15, a portion for engagement with the springs 14.
Recently, the whole structure including the valve guide 3 is such that the guide pin 7 is omitted for cost reduction and in view of shapes of for example the cross head 5 and stem seal 11.
When the engine is driven, one end of the rocker arm 6 is pushed upward by a push rod (not shown) during exhaust stroke of the engine and at the same time the other end of the arm 6 is pushed down to open the valve 1 via the cross head 5 to thereby discharge the exhaust gas from a combustion chamber (not shown).
In this connection, typical structures of the valve guide are shown by some patent publications (see, for example, Reference 1).
[Reference 1] JP 7-34816A